Spore-producing fungi served in tony restaurants grow in a number of mediums—including coffee grounds. That tidbit of knowledge started two guys on a business venture that diverts 10,000 pounds of coffee grounds a week from the landfill so that it can be turned into soil for the ‘shrooms. And they’re just getting started.

"We both understood the potential scope for it," Nikhil Arora, one of the company’s co-founders, told Grist. "This country is addicted to drinking coffee day in and day out. We knew if we could turn this waste into something of value, it could make a huge impact."

The company, Back to the Roots (BTTR), started in 2009 when Alex Velez and Arora, then students at the University of California, Berkeley’s Haas School of Business, heard their professor describe a project in which women grew mushrooms in coffee grounds to stave off malnutrition. With the help of Alan Ross, a professor, mycologist Paul Stamets, and consultants, the idea grew into an enterprise. Now the men and their four employees sell gourmet mushrooms and mushroom-growing kits from the company’s San Francisco locale.

BTTR’s delicious and decidedly non-coffee flavored mushrooms are helping the company thrive. The outfit produces more than 600 pounds of oyster mushrooms a week, which are grown primarily from grounds procured from Peet’s Coffee & Tea stores. After the company turns the grounds into compost and grows the product, Whole Foods and the Berkeley Student Coop sell BTTR’s produce. Those who want to try their hand growing their own mushrooms can buy the kits online.

Their website explains what purpose they hope to serve with their fungi: “Our vision is to serve as a standard bearer of innovation and responsibility in our community in order to inspire others to work towards a more sustainable future.”

Arora and Velez are not the first two business-minded entrepreneurs to work with mushrooms. Eben Bayer and Gavin McIntyre grew mushrooms in college to create insulation. Now their company, Ecovative, grows biodegradable packaging. Even though the two ideas are very different, they both show how fruitful—and sustainable—work with fungi can be.